In inkjet printers, a coloring agent is generally defined as a material that exhibits a unique color by selectively absorbing or reflecting visible light. Coloring agents can be divided generally, into dyes and pigments.
A dye is a coloring agent that is printed on and absorbed into a material such as fiber, leather, fur, paper, or the like, so that the printed material has color fastness with respect to light, rubbing, and the like. A pigment is a micro particle having a coloring agent, and is not directly absorbed into but is instead adhered to the surface of a material using a physical method, such as adhesion or the like, so that the printed material has a unique color.
Dyes are mixed and dissolved in solvents such as water; or the like, but pigments are generally not dissolved in the solvents. Therefore, a crucial aspect for forming pigments is to uniformly disperse pigment particulates in solvents and thereby, allow the formed dispersed state to remain stable permanently without re-aggregation.
Water-soluble dye-type ink is superior in terms of long-term storage stability, it keeps its uniformity and has good color clarity and brightness. However, this ink may be poor in waterfastness, lightfastness, etc.
Pigment type ink has high optical density (OD), good waterfastness and lightfastness, and little bleeding among colors. However, this ink has poorer color tone clarity and has weaker stability in terms of long-tern storage than the dye-type ink. In addition, images which are printed using the pigment type ink have poor dryfastness and wetfastness; that is, they have poor rubfastness.
Also, when printing in color (multicolor printing) with dyes or pigments, bleeding may occur at interfaces of the colors, thereby reducing clearness of printed images.
To enhance the rubfastness, resin has been added to ink. However, the viscosity of ink may be increased as a result. To prevent the increase in the viscosity of ink, resin particles have been added. However, because resin particles and pigments are separately dispersed in an ink formed using these methods, this may not be sufficient.
A capsulated coloring agent improves the performance of printed images, including characteristics such as rubfastness, waterfastness, and the like. However, a greater concentration of polymer resins may be generated in an aqueous solution during the capsulation process. Thus, the capsulated coloring agent may clog a nozzle surface when used in an ink cartridge. In addition, during long periods of storage, physical properties of the ink may change, such as an increase in the viscosity of the ink due to the polymer resin in the aqueous solution.
There is a need for an ink composition which has excellent storage stability like water-soluble dye-type ink, has excellent waterfastness like pigment type ink, and also has improved printed gloss and rubfastness. There is also a need for improving properties of an ink composition by modifying a colorant used therein.